Drinking water has been, and continues to be, heavily treated for bacteria and other microscopic organisms that may cause infection in humans and other animals subsequent to consumption. In order to disinfect water supplies, halogenated materials have been introduced therein that have proven more than adequate for such a purpose. Unfortunately, although such halogenated compounds (chlorinated and chlorinated types, primarily) exhibit excellent disinfection capabilities, when present within aqueous environments at certain pH levels these halogenated compounds may generate byproducts that may themselves create health concerns. The United States Environmental Protection Agency (USEPA) in fact currently regulates four types of trihalomethanes (THM4) and five specific types of haloacetic acids (HAA5) within drinking water. These THM4 are chloroform, bromoform, dibromochloromethane, and bromodichloromethane, and these HAA5 are monochloroacetic acid, dichloroacetic acid, trichloroacetic acid, monobromoacetic acid, and dibromoacetic acid. Removal of such compounds from drinking water is not possible as for typical chlorinated disinfecting compounds, at least not at the same reliability level as for the disinfecting agents (the brominated species listed above may occur as the result of certain chlorinated acids and/or ions reacting with brominated compounds present within the drinking water prior to disinfection or hypobromous acid). Thus, residual amounts may remain within treated water supplies that may require further removal processes to be undertaken. Of course, if the level of contamination is sufficiently low, initiation of such potentially expensive removal steps would be unwise from an economic perspective.
The USEPA currently has set a maximum contaminant level for these THM4 in drinking water at 0.080 mg/L and for these HAA5 in drinking water at 0.060 mg/L (four other haloacetic acids are currently not regulated by the USEPA, bromochloroacetic acid, bromodichloroacetic acid, dibromochloroacetic acid, and tribromoacetic acid; including these, the total haloacetic acid group is known as HAA9). It is thus important to reliably analyze and measure the total amount of such contaminants in order to determine if removal if necessary. The USEPA has instituted its own testing methods for such a purpose. Four such methods are currently in practice to measure HAA5 levels: USEPA 552 and 552.2, which involve the liquid-liquid extraction of haloacetic acids from water sources into methyl-t-butyl ether, followed by derivatization with acidic methanol to form the corresponding haloacetic acid methyl esters. Analysis by gas chromatography-electron capture detection provides reliable measurements of the haloacetic acid amounts present within the subject water supply. The USEPA 552.1 test protocol employs ion-exchange liquid solid extraction, subsequent derivatization into methyl esters, and similar gas chromatography-electron capture detection. The other, USEPA 552.3, is a derivative of the first with optimizations of acidic methanol neutralization procedures for improvement in recoveries for brominated trihalogenated haloacetic acid species. However, these general processes have been found to have numerous drawbacks. For instance, injection port temperature can affect debromination of certain haloacetic acid species (particularly tribrominated types) that may lead to underrepresentation of the amount of such contaminants present within the tested water source. Likewise the water content of the methyl-t-butyl ether extract may dicarboxylate the haloacetic acids, again leading to an under-reporting of the actual amounts present within the test sample. Furthermore, the involved processing needed to actually undergo such analysis makes an on-line protocol rather difficult to implement, particularly when hourly sampling is necessary. Other derivatization methods have been either followed or suggested for gas chromatography analyses of drinking water sources as well, including utilizing diazomethane, acidic ethanol, and aniline. Such reactant-based measurements, however, all suffer the same time and labor-intensive problems as with the two USEPA test procedures noted above. As such, on-line analysis through these protocols are difficult, expensive, and labor intensive to implement and run.
Measurement at the source (i.e., within a water purification plant location) may be effective for system-wide average readings; however, in the large supplies of water at such locations, the chances of proper sampling to that effect may be suspect since the contaminants may be present in varied locations, rather than homogeneously mixed throughout the tested water supply itself. Additionally, testing may not uncover the actual level of residual THM4 and/or HAA5 disinfection byproducts prior to the water supply being disbursed to distant dispense sites (transfer pipes, homes, schools, businesses, etc.). In any event, there is a relatively new rule in place that requires utilities to provide evidence of compliance with trihalomethane or haloacetic acid levels at multiple locations, rather than a straightforward system-wide average. Thus, since the above-described derivatization procedures with gas chromatography-electron capture detection analytical methods are not suitable for a uniform trihalomethane/haloacetic acid measurement scheme. There is thus a drive to implement remote testing via real-time, on-line methods for in water supply HAA5, and, more importantly, for HAA9 contaminant level measurements, in addition to the THM4 contaminant levels as well.
Such a desirable on-line procedure has been difficult to achieve, however, particularly as it pertains to the determination of not only the total amount of THM4 and HAA9 within water supplies, but also the amount of each species of THM4 and HAA9 groups present within the tested water source. High performance liquid chromatography, utilizing electrospray ionization-mass spectrometry or ultraviolet absorbance for detection, has been attempted, as well as ion chromatography, with membrane-suppressed conductivity detection or ultraviolet absorbance detection. Other attempts with inductively coupled plasma-mass spectrometry and electrospray ionization-mass spectrometry coupled with ion chromatography have been attempted for this same purpose. The detection level can be as low as 0.5 to less than 10 μg/L for HAA9 species, but only subsequent to sample preparations. The sensitivity and selectivity of ion chromatography and high performance liquid chromatography methods are negatively affected without the cumbersome sample preparations in place, therefore requiring operator intervention during analysis. Again, this issue leads to serious drawbacks when on-line implementation is attempted as well.
Another methodology that has proven effective is post-column reaction-ion chromatography. This has shown promise, but only in terms of quantifying bromate ion concentrations in drinking water samples at a single μg/L level. This dual selectivity form (separation by ion chromatography column as well as the selective reaction with the post-column reagent with the analyte) offers an advantageous test method over the others noted above, except for the presence of more common anions, specifically chloride, at much higher concentrations within the sampled drinking water supply (mg/L instead of μg/L). It was then undertaken to combine the separation capabilities of ion chromatography with the reaction of the haloacetic acid species with nicotinamide, followed by fluorescence detection to measure the individual and total HAA5 concentrations in drinking water at the single μg/L level. The problem with such a protocol, unfortunately, was that bromochloroacetic acid interfered with dichloro- and dibromo-acetic acid quantifications. Despite this problematic limitation, it was determined that fluorescence detection provided a much-improved detection protocol in comparison with ultraviolet and mass spectrometry possibilities. Thus, although such a fluorescence method of detection, coupled with the post-column reaction (again with nicotinamide reagent) and ion chromatography, exhibited the best results in terms of an on-line test method for HAA5 drinking water contaminant measurement levels, there remained a definite need for improvements in total trihalomethane and haloacetic acid measurements and identifications within such test samples. To date, however, there has not been an analytical test protocol that has permitted implementation of such a system within an on-line, real-time monitoring procedure with an acceptable degree of reliability. An automated system that provides such versatility and reliability has simply not been forthcoming within the pertinent art.